In mobile terminals such as a mobile phone, a microphone of the mobile terminal may be affected by electrical noise generated by the mobile terminal itself. For example, a noise level of a voice signal output from a microphone may increase because of noise generated by various kinds of electrical components such as a transceiver circuit and a liquid crystal display unit, which are equipped in the mobile terminal.
In order to reduce the noise generated by various kinds of electrical components in a mobile terminal, for example, Patent Document 1 describes a noise prevention method which reduces high frequency noise generated by circuit boards which are equipped in a mobile information terminal. In the noise prevention method described in Patent Document 1, the high frequency noise generated by the circuit boards which are equipped in the mobile information terminal is reduced by arranging a conductive substance between the circuit boards, or by forming a conductive substance with metallic foil or metallic plating applied to a housing surface.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-264355 (Paragraph 0037 to 0042, FIGS. 2 and 3)